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The question often comes up about how to make an animation in BRL-CAD. As BRL-CAD is primarily a solid modeling system for engineering and analysis purposes, there is (presently) only limited support for generating animations but it is possible with the assistance of some third-party tools. The basic method is to make your model, decide what keyframes and sequencing you want to have in your movie, render those keyframes as images, and then composite them into an animation. BRL-CAD can help will all but the last compositing step.

So basically you need to render frames for your animation and then composite them together into a movie.

There are a variety of rendering and image processing tools that support a wide range of visualization techniques. Tools that may be of interest include rt, rtedge, rtxray, pixmatte, and pixblend as well as a variety of other rendering and image processing tools.

If the animation you want is very simple like having an animation of something spinning, the relatively simple process is described in the #Fly-around animation section. If, however, what you want to animate is considerably more complex, there are a variety of tools that become important for setting up animation paths, managing keyframes, interpolating between frames, and previewing the animation. There are animation tools in MGED (see the 'animmate command' (yes, it's actually spelled that way) for starters, the AnimMate Control Panel (under Tools), as well as a variety of animation table processing tools outside of MGED.

It can be really easy to make a simple fly-around animation of your geometry. The rt command has options for azimuth and elevation that will let you render animation frames around a given object. The first step is to render your images. You can create a shell script like this:

This renders 36 images of the object top_level_object from a geometry database that was named database.g, creating images every 10 degrees (azimuth) at an elevation of 35 degrees. The images are named image000.png through image350.png.

Walking through the shell script, the second line (for i in `loop 000 359 10` ; do) just sets up a loop to run with variable i set to the next number each pass through the for loop. You can see the expansion by running the loop command directly:

The third line calls rt to render an image. The -a option sets the azimuth value and the -e option sets the elevation value. The -w and -n options set the width and height of the image respectively. The -o option specifies the filename for the output image that is generated. Finally, there is the name of the database to read from and the name of the object in that database that we want to render. The object is automatically centered in the view.Please make sure that the commands loop and rt are in the your search PATH using the linux export command.

Once you run the script and have generated your image frames, you're done with BRL-CAD. The next step is to take those image frames that were rendered and provide them as input to any number of tools that will generate a movie for you.